1. Field of Invention
The invention relates to personal security systems including routines for locating emergency transmissions, and to the selective testing of such systems for proper operation. More specifically, the invention relates to security systems including a network of communications devices, and to apparatus for testing the devices and communications between the devices.
2. Description of the Prior Art
Personal security devices come in many varieties, ranging from noisemakers that scare, to irritant sprays that deter and signal transmitters that call for help.
A number of recently proposed and more sophisticated systems include portable radio frequency transmitters carried by a system subscriber for actuation in emergency or threatening situations. Fixed receivers monitor the area where the system is installed and initiate a planned sequence of events when an emergency transmission is detected. Sirens and strobes may be energized to scare away attackers while a call is made for assistance from appropriate security personnel. The system usually is monitored from a control station including a program for identifying the approximate location of the threatened subscriber using the known positions of the receivers that detect the transmission. Examples of these and similar approaches are disclosed in Shields U.S. Pat. No. 4,998,095, issued Mar. 5, 1991; DeMarco U.S. Pat. No. 4,764,757, issued Aug. 16, 1988; and Levinson U.S. Pat. No. 4,611,198, issued Sep. 9, 1986. An improved approach for more precisely locating the transmission is disclosed in Kostusiak U.S. Pat. No. 5,115,224. In addition to the known positions of the monitoring receivers, he uses the relative strengths of the signals compared between several receivers.
Testing is an important feature in security systems, and many alternatives are available. Reich et al. U.S. Pat. No. 4,908,602, issued Mar. 13, 1990, discloses a personal emergency response system, somewhat similar to those mentioned above, including a momentary action button on a fixed receiver for selectively placing the system in a test mode. Testing of the communications link between the portable transmitter arid the receiver will not then initiate the alarm. Tamura et al. U. S. Pat. No. 4,694,282, issued Sep. 15, 1986, also discloses a test mode in a security system, this time actuated by a switch on affixed transmitter. Tamura et al. transmit test signals to a receiver at a level representing a worst case environment.